The present invention relates to a device and method for the continuous heating of a liquid to a constant temperature. A particular application of this invention is the heating of a liquid such as waiter to a constant and precise temperature to allow, for example, the preparation of food. In particular, this device and this method may be used to advantage for heating water under pressure for making coffee.
For making coffee, discontinuous water-heating devices in which a given amount of water is heated, then used with the aid of a pump to make the coffee, are known. In such devices, the volume of water available is limited, the heating time is long and it is inevitable that there will be a period of waiting between each making of coffee. In addition, these devices are bulky and expensive.
There also exist some devices for the continuous heating of water, where the water is heated as it passes along a duct or pipe embedded in a block with a high heat capacity to guarantee constant temperature. The volume of water that can be used is limited by the heat capacity of the block, and in any event the devices needed to regulate the electrical power supply and/or the amount of water delivered are not capable of achieving sufficient temperature precision using economical means. Again, the heating time is long.
Such devices for the continuous heating of water for making coffee are known, for example, from the following documents: EP 0 307 955, EP 0 676 163, EP 0 771 542 and FR 2 683 135. Despite these disclosures, there still remains a need for improvements in continuous heating devices for liquids.
The present invention relates to a device for the continuous heating of a liquid to a constant temperature which device is economical, precise as regards the temperature at which the liquid is let out, the heating unit of which does not require high thermal inertia and which does not therefore require a long time for heating of the liquid.
The device and method of the present invention for the continuous heating of a liquid to a constant temperature obviates the disadvantages of the known devices and makes it possible to achieve the aforementioned goals.
Thus, the invention specifically relates to a device for the continuous heating of a liquid to a constant temperature. The device includes a reservoir of an ambient temperature liquid, a pump having an inlet and outlet, a heating unit, a heated liquid outlet for delivering heated liquid at a preselected temperature, a control device for regulating flow of liquid delivered by the pump to the heating unit, a recalculation device for recirculating liquid leaving the heating unit to one of the reservoir or the inlet side of the pump when the liquid has not reached the predetermined temperature, and a rated valve on the heated liquid outlet for sensing the temperature of the heated liquid before delivering it from the heating unit.
Advantageously, both the control device and recirculation devices are controlled based on the temperature of the liquid leaving the heating unit. Preferably, the control and recirculating devices are combined into a single unit, and a thermostatic element which reacts in response to the temperature of the liquid leaving the heating unit to control the operation of the control and recirculation devices to assure that heated liquid is delivered at the preselected temperature.
The combined control/recirculation unit preferably comprises a first (or cold) part formed of a first body comprising an inlet for liquid delivered by the pump, an outlet for liquid to pass to the heating unit, and a flow control nozzle having a structure which can alter liquid flow to the heating unit. The combined control/recirculation unit further comprises a shut-off nozzle, a second (or hot) part comprising a second body coaxial with, secured to and thermally insulated from the first body, an inlet that receives liquid leaving the heating unit, a chamber that is in fluid association with the second body inlet to receive liquid therefrom, the chamber further being in fluid association with the heated liquid outlet and being connected, via the shut-off nozzle, to a recirculation outlet that is in fluid association with the pump inlet, and the chamber housing the thermostatic element.
The thermostatic element preferably includes a piston, and the combined control/recirculation unit includes a first bore in the first part of the unit, second, larger bore in the second body of the unit, a rod member having a body which is slidably received in the first bore and a head that is of larger size than the body that is received in the second bore, and a spring operatively associated with the rod head and thermostatic element, such that the piston acts on the rod head against the action of the spring to position the rod in the respective first and second bores depending upon the temperature of the liquid therein so that the nozzles can direct the liquid to achieve the predetermined temperature prior to allowing the heated liquid to exit the heated liquid outlet.
The first body preferably comprises an inlet chamber in fluid association with the pump inlet and an output chamber in fluid association with the heated liquid outlet, and the nozzle includes a radial slot opening onto the periphery of the rod, the cross section of which varies along the longitudinal axis of the rod, this slot making it possible, depending on the axial position of the rod, for the inlet chamber to be connected to the outlet chamber by passages of different cross sections, and in that when the rod is in the position of rest, the passage cross section is at a minimum. Advantageously, first and second seals are operatively associated with the rod and are located in the first and second bodies, respectively.
In a preferred embodiment, the rod head includes a radial milling opening on its periphery and over part of its length which, depending upon the axial position of the rod head in the second bore, either fluidly connects the chamber of the second body to the recirculation outlet or prevents such fluid connection. In this arrangement, the second seal is located between the chamber and the recirculation outlet.
The device may include a switch, with the heating unit having an electrical power supply that is controlled by the switch, and the temperature sensor operatively associated with the switch. Also, the heating unit preferably can be one that has low thermal inertia, the liquid can be water and the heated liquid outlet is in fluid association with a percolator for brewing coffee.
The thermostatic element is preferably one of the wax cartridge type, liquid vaporization type, is based on a shape-memory metal or is based on a metal having a high coefficient of expansion to facilitate axial displacement. Also, the device may include a temperature sensor mounted on the recirculation device for controlling electrical power to the pump. In another preferred arrangement, the flow control nozzle includes a passage having a variable cross-section for regulating the flow rate of liquid delivered to the heating unit continuously or in discrete increments.
The invention also relates to a method for the continuous heating of a liquid to a constant preselected temperature. The method includes the steps of delivering a quantity of ambient temperature liquid to a heating unit for heating of same, sensing the temperature of the heated liquid leaving the heating unit to determine if it has achieved the preselected temperature, and delivering heated liquid that has achieved the preselected temperature.
Advantageously, the heated liquid is recirculated to the heating unit until the heated liquid has achieved the preselected temperature. The liquid is preferably delivered by a pump to a heating unit that has low thermal inertia, and the heated liquid is recirculated to the pump if the preselected temperature is not achieved.
Also, the delivery of liquid to the heating unit can be regulated to a minimum value that is significantly below that which represents an amount of liquid that can be heated to the preselected temperature by the heating unit, with the recirculation being continued until the heated liquid achieves the preselected temperature. When the temperature of the liquid leaving the heating unit is sensed as meeting or exceeding the preselected temperature, the delivery of liquid to the heating unit can be increased. Preferably, the sensing of the liquid temperature is utilized to control the flow of liquid from the pump to the heating unit as well as for the recirculation of the heated liquid to the pump.